1. Field of the Invention
The present invention relates to a register correspondence method in a logic equivalence verifying system.
2. Description of the Related Art
As verifying functions of circuits, use is generally made of simulation methods. Particularly, if the function of a circuit is written in hardware description language (HDL), a designer recognizes the function of circuit by a simulation method. Then, the designer designs a new circuit by modifying the HDL written circuit using a logic synthesis system or manually. In this case, the designer again verifies the function of the new circuit by a simulation method with reference to the result of the above-mentioned simulation method.
In the above-mentioned verifying method using simulation methods, however, if the circuit becomes remarkably large, it takes a long time to verify the circuit since a large number of test patterns are required.
In order to reduce the verifying time, a prior art logic equivalence verifying system for directly comparing circuit information with reference circuit information has been developed (see JP-A-8-22485).
In this logic equivalence verifying system, a circuit analysis section analyzes two kinds of circuit information to recognize external terminals, registers and combination circuits from each of the circuit information. Next, a register correspondence section makes a register correspondence between two kinds of the circuit information automatically or manually. Next, a logic extraction section extracts logic information of the combination circuits of the two kinds of circuit information as a binary decision diagram (BDD) for every verification point. This will be explained later in detail.
However, if the register correspondence section of the prior logic equivalence verifying system is forcibly applied to a sequential circuit having a feedback loop, the register correspondence processing time is increased.
Further, in the prior art register correspondence, if test circuits are added in circuit information, it is impossible to make a register correspondence.